1. Field of the Invention
This invention relates generally to a method of transmitting digital data using a compact digital disc and, more particularly, to a method of recording information other than two-channel audio signals on such disc and reproducing same with enhanced error correction capability.
2. Description of the Background
The systems known as compact audio disc systems are now well known and such systems employ an optical-type digital audio disc from which high quality stereophonic musical signals can be reproduced. The total memory capacity of this kind of compact disc is approximately 500 Mbytes and, thus, the compact disc would seem to lend itself for storage of information other than strictly audio information. Moreover, because the playback apparatus is already in existence then it would be advantageous to employ such compact disc bearing information other than audio information to produce visual information such as charts and statistics using graphics and other pictorial illustrations by means of still picture displays. The use of such compact disc to provide video game apparatus would also seem to be a desirable feature.
Nevertheless, in the known digital audio disc systems, the error correction coding processing is performed on a per byte unit basis by dividing 16 bits of one data sample into two groups, the higher significant eight bits and lower significant eight bits and the interleaving, deinterleaving, coding, and decoding processings using Reed-Solomon codes are all carried out on such byte-unit basis. Thus, error correction coding can be relatively easily executed with respect to the digital audio signals and would also seem to be the case with respect to the digital data signals. Nevertheless, a common practice in the digital audio signal art for correcting errors is to undertake interpolation processing, such as mean value interpolation, that interpolates a missing data point based on adjacent data points, however, such error processing is not available when reproducing signals other than musical signals, because there is very low correlation among such data. Thus, it is almost mandatory that the error rate of reproduced data be better than that of the reproduced musical signals. In that regard, the error rate which is used in storing digital data is generally required to be around 10.sup.-13 or less, whereas the error rate for an existing compact audio disc is approximately 10.sup.-11.
The reproduction signal processor used in presently known compact audio disc systems is constructed largely utilizing large scale integration (LSI) chip circuitry and, thus, it is desirable that the necessary increase in error rate be realized utilizing substantially the same kind of signal processor circuitry present in the now available compact audio disc players.
One code that is known to have high error rate correction capability that might be used for transmitting digital data via the digital disc is the code formed by the combination of the cross-interleave and the Reed-Solomon code (CIRC), and this code has been adopted for the compact audio disc. In using such error correction approach for data other than audio data, a code similar to this code (CIRC) would be preliminarily imparted to the digital data and then the digital data supplied to an encoder of the compact disc system, however, when the interleave is executed on a byte-unit basis a problem arises in that the address control necessary to perform the interleaving processing becomes overly complicated. On the other hand, if the interleaving were to be carried out on a word-unit basis, the interleaving process is simplified but the informational bit length becomes excessively long and the arrangement of the encoder becomes exceedingly complicated. Moreover, in this such situation the time required to accomplish coding and decoding processing becomes excessively long.